The present invention relates to stone rollers, particularly for paper making machines. Such a roller includes a roller body of stone with clamping plates arranged at its axial ends, and the plates are connected to each other through the roller body and hold the body under axial stress. An example of such a roller can be found in U.S. Pat. No. 3,737,962.
Stone rollers of this type are used particularly as press rolls in the press sections of paper machines. However, they may also be used in other sections of the paper machines, for instance in the dry end or in calenders.
The body of the roller is normally comprised of granite. In operation, the stone roller rests with a predetermined pressure against a counter-roller. As a result, the stone roller, which is several meters long, is stressed in flexure between its end support points. In order to prevent the stone body from breaking apart, it is clamped between clamping plates arranged at its ends. For the clamping purpose, an axial tie-rod positioned at the middle or axis of the roller is used to draw the clamping plates together. The tie-rod is given an initial static stress, usually a few hundred t (150-1200 t). 1 ton=1000 kg. oscillating load, which derives from the forces of reaction of the rotating roller on its end supports. The traditional construction of a stone roller therefore requires a correspondingly large tie-rod of very great weight which must be manufactured as a special forged part for each roller.
Tie-rods placed at the center of the roller could have much smaller cross-sections if they only had to transmit the initial static stress. But, experience has shown that these tie-rods break during operation since they receive an additional alternating load from flexing forces. Breaking of the tie-rods usually occurs at places having notches, and, therefore occurs at the clamping threads on the rods. These difficulties have previously been eliminated by making the cross-sections of the single centrally disposed tie-rods considerably larger. But, this has resulted in greater weight and higher expenses.
In addition, the steel clamping plates which transmit the initial force from the tie-rod to the stone roller, at the ends of the roller, must usually be very thick since they have to take up a high bending or inversion moment. The thickening of the plates has the disadvantage that for the stone roller, there is an even greater distance between the end supports than with customary rollers of a paper machine. The tie-rod can additionally be surrounded by filler material in the borehole which contains it.
Another type of known roller that uses a tie-rod is the drying cylinder of a paper machine, as shown in U.S. Pat. No. 2,576,036 and West German Provisional Patent (Auslegeschrift) 1,160,723. Here, the tie-rod serves merely to relieve the cylinder heads which are acted on by steam pressure.